JPH0474733B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for improving the power factor of a power supply circuit, and in particular, the present invention relates to a method for improving the power factor of a power supply circuit. The present invention relates to a power factor improvement method for improving power factor reduction caused by a smoothing circuit in a power supply circuit that supplies power to a load.

[Conventional technology]

First, a conventional power factor improvement method will be explained with reference to FIGS. 1 and 2.

Figure 1 shows the power factor correction device previously developed to improve the power factor of this type of power supply circuit (this type of device is disclosed in Japanese Patent Application Laid-Open No. 17931/1983), and the second
The figure is an explanatory diagram of its basic operation. In Figure 2, A is the AC voltage Vs, B is the AC current Is before power factor improvement, C is the AC current Is after power factor improvement, and D is the drive signal VB.
This shows that.

In FIG. 1, 1 is an AC power source, 2 is a power factor correction circuit, and 3 is a rectifier circuit.

The DC output of the rectifier circuit 3 is smoothed by a capacitor Cd of the smoothing circuit and supplied to the load 4. Here, the load 4 is generally an inverter or a DC motor.

The power factor improvement circuit 2 includes a reactor Ls related to inductance, and diodes D3, D4, D5, and D6.
and a transistor T related to the switching element.
1 and are connected as shown in the figure.

Note that D1, D2, D3, and D4 are diodes that constitute a rectifier circuit, and D3 and D4 also serve as elements of the power factor correction circuit 2.

The operation of the power factor correction circuit 2 having the above configuration will be explained with reference to FIG. 2.

A in the figure indicates the AC voltage Vs of the AC power supply 1, as described above.

Also, the AC current Is flowing out from the AC power supply 1 is
In the absence of a power factor correction circuit, a pulsed current flows only near the peak value of the AC voltage Vs, as shown in FIG. 2B.

This is because, as mentioned above, the DC output of the rectifier circuit 3 is smoothed by the capacitor Cd.

Further details of the reason are as follows.

Here, with reference to the circuit shown in FIG. 1, a case will first be described assuming that the power factor correction circuit (reactor Ls, diodes 5, 6, transistor T1) 2 is not provided. When the capacitor Cd connected to the output side of the rectifier circuit 3 is charged near the peak value of the AC voltage Vs, the AC voltage that falls outside of the peak value as time passes is shown in Figure 8. As shown, it becomes smaller than the smoothed voltage Ed of capacitor Cd. Therefore, the diodes constituting the rectifier circuit 3 become non-conductive in a reverse bias state, and no alternating current flows. And capacitor Cd
The DC voltage Ed depends on the size of the load 4,
It gradually decreases, but in the next half-wave period, when the AC current Vs again becomes larger than the DC voltage Ed near its peak value, the diode of the rectifier circuit 3 becomes forward biased, and the AC current Is flows again to the capacitor.
CD is charged.

As described above, in the capacitor input type rectifier circuit, there is a region where the alternating current voltage is smaller than the direct current voltage charged in the capacitor, so the alternating current becomes pulsed.

As described above, since the alternating current Is has a pulsed waveform, it contains many harmonic components, and therefore the power factor as seen from the alternating current power supply 1 is usually poor at around 60%.

Therefore, in order to make the waveform of the alternating current as sinusoidal as possible and improve the power factor, the voltage when looking at the alternating current side from the rectifier circuit should be made larger than the direct current voltage so that the alternating current flows. For this purpose, a power factor correction circuit (boost chopper) 2 consisting of a reactor Ls, a switching element T1, etc. shown in FIG. 1 is used.

When the power factor correction circuit 2 is operated, the alternating current Is becomes as shown in Figure 2 (c), and the current flows even during periods when it would not normally flow, and the waveform becomes a sine wave overall. As the power approaches , its harmonic components decrease and the power factor increases.

That is, if the transistor T1 is turned on and off according to the drive signal VB shown in FIG. Short-circuited, the alternating current Is gradually increases.

After that, if the transistor T1 is turned off, the electricity (boost) stored in the reactor Ls immediately before turning off
Due to the energy, the alternating current Is flows into the capacitor Cd through the rectifier circuit 3 and gradually decreases.

[Problem to be solved by the invention]

In the power factor improvement circuit 2 that performs the above basic operation, the second element determines the power factor improvement effect.
As shown in FIG. 2, the ratio of the on time Ton to the switching period Tc of the switching element T1, that is, the conduction rate Dc (=Ton/Tc×100) is mentioned. Note that TA shown in Figure 2 D is the AC voltage Vs
This is the total chopper operation period (chopper operation range) during which the switching element T1 is turned on and off in one cycle. Second
As shown in Figure C, the limit value IsL when the alternating current Is is constant
In the region near the peak value of the alternating current, which exceeds the current, the switching element T1 is turned off and there is a chopper stop region (stop period), and the region excluding this chopper stop region is the chopper operation period.
Become a TA.

By the way, the conductivity Dc is determined by the size of the load 4,
In other words, the optimum conduction rate that maximizes the power factor changes depending on the magnitude of the DC current Id shown in Figure 1, but conventionally, this point has not been considered. .

In other words, in the conventional power factor improvement method, the conduction factor
When selecting Dc, the conductivity factor Dc that maximizes the power factor is uniquely selected based on the rated state of load 4, and the conductivity factor Dc after selection is independent of the state of load 4. It was always constant. For example, JP-A-53-
In the conventional technology disclosed in No. 17931 and Japanese Unexamined Patent Publication No. 17932, a reference voltage is uniquely set using a manual variable resistor, and this reference voltage is compared with a triangular oscillation wave having a higher frequency than that of the commercial power supply. A specific conduction rate is set according to the rated load of the electrical equipment to be controlled.
I had decided on DC.

Therefore, when the load changes during operation, depending on the magnitude of the load, there are regions where sufficient power factor improvement cannot be achieved.

Here, the problem will be explained in detail.

When using this type of power factor correction circuit, the conduction factor Dc of the switching element for chopper operation should be set so that the power factor is maximized according to the rated value of the load, and should always be kept constant in other operating ranges as well as the rated value. Then, when the load becomes lighter than the rated value, the following phenomenon occurs because the conduction rate Dc is fixed even though the load current (DC current) has become smaller. In other words, as shown in Figure 9, the chopper operation of the power factor correction circuit converts the current into a capacitor.
In the region supplied to Cd, the current is forcibly supplied at the same level as the rated value, and the chopper stop region (alternating current Is
(near the peak value of the wave), the current level drops due to a corresponding decrease in the load current, and as a result, the current in the chopper operating range increases more than the alternating current in the chopper stop region, causing distortion in the entire waveform of the alternating current Is. occurs. Therefore, since the third harmonic component increases, the power factor decreases on the contrary. In addition, there was a risk that the voltage step-up would become excessive and the DC voltage Ed would rise abnormally.

Conversely, when the load increases, the increase in load current is reflected in the chopper stop region (near the peak value of the alternating current), and the current in this region becomes too large compared to the current during the chopper operation period. In this case, the alternating current waveform approaches the pulsed waveform shown in FIG. 8, and the power factor decreases.

That is, according to the conventional power factor improvement method, it is technically difficult to improve the power factor of a power supply circuit equipped with a capacitor input rectifier circuit as described above over a wide range of loads.

The present invention has been made in view of the above points, and
The purpose is to solve the problems of conventional technology, to automatically maintain a high power factor even when the load size changes during operation, or to be able to be used as is in various equipment with different loads. However, it is an object of the present invention to provide a power factor improvement method that automatically enables high-efficiency operation without manually adjusting the conduction rate using a variable resistor as in the past.

[Means to solve the problem]

In order to improve the power factor, the present invention focuses on the fact that the optimum conduction factor of the chopper switching element changes depending on the magnitude of the load, and performs the following power factor improvement control.

That is, to explain the present invention by quoting the symbols used so far, an AC power supply 1 is connected to a rectifier circuit 3,
This is a power supply circuit that converts the DC power into DC power by a smoothing circuit having a capacitor Cd and supplies the DC power to the load 4. It is equipped with a power factor correction circuit 2 composed of an inductance element Ls, a switching element T1, etc., and this switching element Due to the chopper operation of T1, the AC current from the AC power source 1 is transferred to the inductance element.
After accumulating electrical energy in Ls, a series of operations are performed to forcibly supply it to the smoothing circuit side.
In the method of improving the power factor of the power supply, a means is provided to detect the size of the load during operation,
Based on this load detection signal Rd, the conduction rate Dc required for the chopper operation of the switching element T1 is determined as follows:
A control circuit is used to automatically perform variable control so that the load increases when the load becomes large and decreases when the load becomes small, and the current conduction rate of the switching element T1 is controlled to adjust the current flow rate of the power supply circuit in relation to the load that changes during operation. This is done by making the AC current waveform close to a sine wave and setting a relational expression that can have a maximum power factor or a power factor close to this.

[Effect]

As mentioned above in [Problems to be Solved by the Invention], in order to improve the power factor of this type of power supply circuit, the optimum conduction factor Dc (maximum power factor or The conduction factor (to obtain a power factor close to .) is not constant, but has the property of varying depending on the size of the load.

Here, the optimum conductivity Dc will be explained based on FIGS. 3 and 5 prior to explaining the operation of the present invention.

FIG. 3 shows the relationship between the DC current (load current) Id, in other words, the conduction factor Dc and the power factor Pf with respect to the size of the load. The experimental data shown in Fig. 3 shows that the chopper operation period TA of switching element T1, in other words, the limit value IsL for determining the chopper non-operation area near the peak value of the alternating current Is, is kept constant, and only Dc is changed. It is something.

As shown in Figure 3, by changing the size of the load (DC current Id), the optimum conduction rate for each load is determined.
DC also changes. In this case, the optimum conduction rate corresponding to the maximum power factor increases proportionally as the DC current Id increases (as the load increases).

As mentioned above, the optimum conduction rate Dc corresponding to the maximum power factor
changes depending on the size of the load, but this means that if the load on the output side of the rectifier circuit 3 increases or decreases,
Since the AC current Is on the input side also changes accordingly,
If the current conductivity Dc is changed according to this change, the alternating current Is will be modified to become closer to a sine wave,
This means that the power factor is improved. That is, the conduction rate Dc becomes a waveform modification element of the alternating current Is.

If the relationship in Figure 3 is replaced with the relationship between the DC current Id and the optimum conduction factor Dc corresponding to the maximum power factor, it becomes an approximately linear relationship with respect to the DC current Id, as shown in Figure 5, for example. , can be approximated by the following formula (Furthermore, Fig. 5 also shows the characteristic line of the limit value IsL for determining the chopper operating range (chopper operating period) TA, which will be explained in the example section) .

Dc=C ₃ Id C ₃ is a constant.

In the present invention, since the power supply circuit with the power factor correction circuit is provided with means for detecting the state of the load during operation, the load detection signal (for example, the detected value of the DC current Id described above) is used to detect the load during operation. You can know the size of the current load on.

Based on this load detection signal, the conduction factor Dc of the switching element T1 of the power factor correction circuit 2 is determined as follows:
The control circuit is used to automatically increase or decrease the conduction rate, and the direction of the increase/decrease control of the conduction rate matches the directionality of the optimum conduction rate characteristic shown in FIG. In addition, the increase/decrease control of the conduction rate Dc in this case is performed using a relational expression that can obtain the maximum power factor or a power factor close to it in relation to the load that changes during operation.
For example, since the above equation is used, even if the load changes, a good power factor can always be ensured and efficient operation can be performed.

〔Example〕

An embodiment of the present invention will be described based on FIGS. 3 to 7.

The power factor improvement method of this embodiment is based on the power factor improvement circuit 2 as shown in FIG. The chopper operation period in which the conduction rate Dc is variably controlled and the control operation of this conductivity Dc is performed.
The limit value IsL for determining the chopper operating range is automatically variably controlled to ensure sufficient TA at all times even when there are changes in load (changes in alternating current Is).

Among these, the control of the conduction rate Dc is the gist of the invention, and is as described in detail in the section of the operation of the invention. That is, as described in FIGS. 3 and 5, when using the switching element T1 of the power factor correction circuit, the optimum conduction factor Dc of the switching element to obtain the maximum power factor or a power factor close to this is determined. teeth,
The relationship is such that it increases in accordance with the size of the load.
The relationship between this optimum conductivity Dc and the load that changes during operation, for example, the DC current Id, can be expressed as the following equation (1).

Dc=C ₃ Id...(1) Here, C ₃ is a constant.

If such a relational expression is used, the power factor correction circuit 2
The switching element T1 automatically performs chopper operation by controlling the conduction rate Dc, which is linearly proportional to changes in load. As a result, the rectifier circuit 3 always responds to changes in the state of the load 4 on the output side of the rectifier circuit 3.
The alternating current Is on the input side is modified to approach a sine wave, and the power factor is improved to the maximum or close to it.

The chopper operation period TA of the switching element T1, which is the object of controlling this optimum conduction rate Dc, can be set over the entire cycle of each cycle of the alternating current Is, or even if the range of TA is limited, the same power factor improvement effect can be obtained. However, in this embodiment, the limit value IsL is used to limit the range of TA from the viewpoint of efficiency.

In other words, around the peak value of Is (a region where the AC voltage Vs is higher than the voltage Ed of the smoothing capacitor Cd), the AC current Is can be secured without intentionally performing chopper operation of the switching element T1, so the limit value is reduced near this peak value. The IsL is used to stop the chopper operation and determine the necessary chopper operation period TA, and in that sense, the IsL serves as a secondary function for efficiently controlling the optimal conductivity Dc.

In addition, when using IsL, it is desirable to variably control IsL according to changes in load in order to always ensure a sufficient chopper operation period (Dc control area) TA.

In other words, the limit value for determining the chopper operating range
If IsL is fixed even when the load size changes, when the size of the AC current Is changes due to a change in the load, it will cause the chopper stop region near the peak value of the AC current Is, and eventually the chopper operation. This is because the width of the period TA fluctuates, and the larger the load (the larger Is), the narrower the chopper operation period TA.

Therefore, in this embodiment, in order to ensure a sufficient chopper operating period TA even when the load changes, the limit value IsL for determining the chopper operating range is controlled to increase or decrease in addition to the magnitude of the alternating current Is. are doing.

In Figure 4, a shows the relationship between the limit value IsL and the power factor Pf when the DC current Id=Id ₁ and b shows the relationship between the limit value IsL and the power factor Pf when Id=Id ₂ (Id ₁ <
Id ₂ ), the peak on the characteristic lines a and b in the figure is the optimum value of the chopper operating range TA.

Figure 5 shows the characteristics of the optimum conduction factor Dc (Id-Dc characteristics) that always provides the maximum power factor for the load size (DC current Id), as well as the characteristics of the efficiency that should be ensured at that time. The limit value IsL (Id-IsL characteristic) for obtaining a good chopper operation period was created based on the data in Figure 4, and the above equation (1) can be expressed as follows by the Id-Dc characteristic.
The following equation (2) can be approximated by the Id-IsL characteristic.

IsL=C ₁ Id+C ₂ ...(2) Here, C ₁ and C ₂ are constants.

In equations (1) and (2), according to experiments, the switching period Tc = 500μsec and the reactor Ls is 2mH.
In this case, C ₁ =2, C ₂ =5, and C ₃ =5.

That is, in this embodiment, by using equation (1) as the main and using equation (2) as a supplement, the optimum conductivity DC control is always automatically controlled within the optimum chopper operation period TA. There is.

FIG. 6 is a specific circuit configuration diagram used for this control, and FIG. 7 is a waveform diagram at each part shown in FIG. 6.

In FIG. 6, the same symbols as in FIG. 1 indicate the same or common elements, and the alternating current Is is connected to the emitter terminal of the transistor T1 and the diode D3
and a low resistance inserted between the anode terminal of D4
Detected by Rs.

The current flowing through the low resistance Rs is the full-wave rectified alternating current Is, and the voltage across the resistance Rs is converted to the amplifier 7.
is amplified to obtain an alternating current detection voltage VIs {FIG. 7E}.

On the other hand, the DC current Id {Fig. 7 A} is detected by the low resistance Rd, amplified by the amplifier 6, and averaged to obtain the DC current detection voltage VId {Fig. 7 B}. .

Reference numeral 5 in FIG. 6 is a triangular wave oscillator, and the output of the triangular wave oscillator 5 is the triangular wave shown in FIG.
Becomes VT.

The operational amplifier 8 corrects the DC current detection voltage VId so as to satisfy the above-mentioned relational expression (1).The output of the operational amplifier 8 and the triangular wave VT are input to the comparator 10 and compared. , chopper signal CH as output of comparator 10
{FIG. 7D} is obtained, and the conductivity Dc of the chopper signal CH satisfies the above-mentioned relational expression (1) with respect to the DC current Id.

On the other hand, the aforementioned DC current detection voltage VID is also input to the operational amplifier 9.

The operational amplifier 9 corrects the DC current detection voltage VID so as to satisfy the relational expression (2) between the DC current Id and the limit value IsL for determining the chopper operating range. AC current detection voltage VIs
By inputting these into the comparator 11 and comparing them, the overcurrent detection signal OVI (FIG. 7) is obtained.

12 is a set priority type R/S flip-flop, and the set terminal S receives the above-mentioned overcurrent detection signal.
A signal obtained from the chopper signal CH via the rise time detection circuit 13 is input to OVI and the reset terminal R.

The output of the R/S type flip-flop 12 is a chip suppressor press signal SUP {FIG. 7}.
The aforementioned chopper signal CH is combined with the NOR circuit 14 to form the drive signal VB {FIG. 7 CH}.

This drive signal VB causes the transistor T
By driving 1, the period TA for each cycle is
A DC-controlled chopper operation was performed at the 7th
AC current Is that approximates a sine waveform as shown in Fig.
is obtained.

As described above, according to the circuit configuration shown in FIG. 6, when the power factor correction circuit 2 is operated, even if the magnitude of the load 4 changes during operation, the optimum power supply is achieved within a sufficient chopper operation period TA. Since the flow rate Dc is controlled, it is possible to always obtain the maximum power factor or a power factor close to it.

In addition, in the embodiment, since the chopper stop region of the transistor T1 is also secured by the limit value IsL,
A secondary effect is that there is no risk of the transistor T1 being destroyed by overcurrent.

In addition, the DC current Id is detected as the magnitude of the load, and the optimal conduction rate Dc of the transistor T1 of the power factor correction circuit 2 is automatically controlled variably according to the DC current Id. If so, the object of the present invention can be achieved not only by the DC current Id but also by other methods, such as operation according to the output power of the inverter that is the load.

Also, as mentioned above, without using the limit value IsL,
Even if the entire area of each cycle of the alternating current is set as the chopper operating range and only the conduction rate Dc is variably controlled according to the load, the same power factor improvement effect as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the conduction rate of the chopper switching element of the power factor correction circuit is automatically variably controlled according to the magnitude of the load during operation, so that it can be applied to a wide range of loads during operation. It can always maintain a high power factor in response to state changes, or even if used as is in various devices with different loads, the conduction factor can be automatically adjusted without manually adjusting each one with a variable resistor as in the past. It has excellent effects such as being able to obtain a high power factor.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the power factor correction device developed earlier, and Figure 2 is an explanatory diagram of its basic operation, where A is AC voltage Vs, B is AC current Is before power factor improvement, and C is power factor. The alternating current Is after improvement, D shows the drive signal VB, and Fig. 3 shows the conduction factor and the magnitude of the load current (DC current) when using the power factor correction circuit shown in Fig. 1. The relational diagrams with the power factor, Figures 4a and 4b, are similarly the relational diagrams between the limit value for chopper operating range determination with respect to the load current and the power factor, respectively.
The figure also shows the relationship between DC current, limit value for chopper operating range determination, and conduction rate, FIG. 6 is a specific circuit diagram provided for one embodiment of the present invention, and FIG. This is a time chart showing the signals of each part in the figure. A is DC current, B is DC current detection voltage, C is triangular wave oscillator output, D is chopper signal, E is AC current detection voltage, F is overcurrent detection signal, 1 is a power suppressor press signal, 1 is a drive signal, and 2 is related to alternating current. Figure 8 is an explanatory diagram of the operating waveforms of the power supply circuit before using the power factor correction circuit. Figure 9
The figure is an explanatory diagram pointing out problems with the conventional power factor improvement method. 1... AC power supply, 2... Power factor correction circuit, 3...
Rectifier circuit, 4...load, 5...triangular wave oscillator,
6, 7...Amplifier, 8, 9...Operation amplifier, 1
0, 11...Comparator, 12...R/S type flip-flop, 13...Rising point detection circuit, 14...NOR circuit, Cd...Capacitor, T
1...Transistor (switching element), Rs...
...Low resistance, Rd...Low resistance (load state detection element),
Ls...Inductance element, Dc...Conduction rate,
TA: Period during which the switching element performs switching operation, Id: DC current, Is: AC current.

Claims (1)

[Scope of Claims] 1. A power supply circuit that converts AC power into DC using a smoothing circuit that includes a rectifier circuit and a capacitor, and supplies the DC power to a load, which has a power factor that includes inductance elements, switching elements, etc. an improved circuit is provided, and after the alternating current from the alternating current power source is stored as electrical energy in the inductance element by the chopper operation of the switching element,
In a method for improving the power factor of a power supply circuit by performing a series of operations forcibly supplying power to the smoothing circuit side, a means for detecting the magnitude of the load during operation is provided, and based on this load detection signal. The conduction rate Dc required for the chopper operation of the switching element is automatically and variably controlled using a control circuit so that it increases as the load increases and decreases as the load decreases, and the conduction rate of the switching element is controlled by: The power supply circuit is characterized in that the AC current waveform of the power supply circuit is made close to a sine wave in relation to the load that changes during operation, and a relational expression is set that allows the power factor to be at or close to the maximum power factor. Power factor improvement method. 2. In claim 1, the means for detecting the magnitude of the load is a power supply circuit that detects a direct current flowing from the capacitor of the smoothing circuit to the load side and outputs this direct current value as a detection signal. power factor improvement method. 3. In claim 1 or 2, the conduction rate Dc of the switching element is controlled to have a linear relationship with the DC current flowing from the capacitor of the smoothing circuit to the load side, which indicates the magnitude of the load. A method for improving the power factor of power supply circuits.